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Iranian President Mahmoud Ahmadinejad addresses the staff next to a poster with a picture of late Ayatollah Khomeini, during a tour of Tehran's research reactor centre in northern Tehran, Iran, Wednesday Feb. 15, 2012.(AP Photo/Iranian President's Office)

"How Close is Iran to Exploding its First Nuclear Bomb?"

Belfer Center Director Graham Allison writes in Scientific American that while it is unclear whether Iran has decided to develop a nuclear weapon, it has over the past decade been "cautiously, but steadily, putting in place all the elements it needs to construct a nuclear weapon in short order."

Allison argues that the best way to prevent Iran from developing a nuclear bomb might be to "aggressively explore the offer made by Iranís president Mahmoud Ahmadinejad last fall to end all enrichment beyond LEU in exchange for the purchase of fuel for its Tehran Research Reactor."